In transmission and reception of data such as streaming data or data for use in applications which need to be executed in real time, from a server to a client mounted on a moving object using a wireless communication line, its throughput (an amount of data per unit time) is greatly affected by the influence of a wireless state such as an electric field strength and fading environment. More specifically, the client has largely different throughputs at the different wireless states. Namely, even if the server performs scheduling of distribution of the same amount of data to each of two or more clients having different throughputs, the different data amounts per unit time are transmitted to those clients respectively. Thus, their respective different transmission times for the same amount of data are required, thus causing low accuracy in transmission efficiency.
Further, as long as the network resource is limited in the wireless communications, the transmission efficiency gets worse as the amount of data for transmission to the clients increases. It is therefore important to perform scheduling after accurately predicting future throughputs so that the network resource can be used efficiently.
An invention disclosed in Patent Literature 1 relates to a system for optimizing the quality of playback of data such as video data which requires real-time processing. A client predicts future conditions of a wireless communication line in accordance with both application data and an evaluation of the quality of wireless communications, in order to ensure the quality of video playback, and then sends to a server a request for the amount of video transmission data depending on the predicted conditions. However, although no problem arises when the client is in a stationary state, when the client moves, the influence of an electric field strength and fading environment cannot be neglected, and, as a result, the predicted conditions greatly differ from the actual conditions.
An invention disclosed in Patent Literature 2 relates to a content distribution control system that distributes content data provided by a server to a client via a relay device. This system predicts a load on the relay device on the basis of the throughput of the client, and generates a distribution schedule in such a way that the predicted load does not exceed a predetermined load amount. However, its object is to use network resources efficiently by increasing the amount of the data transmission which is carried out within an off-peak time period during which the network traffic is very small (for example, within a time period between midnight to early morning). For types of the data, no real-time processing is required, and it is further assumed that the generation of a distribution schedule is carried out on a day-by-day basis.